Heat transfer causes various problems of reducing comfort in a building, such as reduction in an air conditioning effect and occurrence of dew condensation. Heat is most easy to transfer on a window in the building. Thus, a multiple glass having high heat insulating properties is desired to be installed on the window. As the multiple glass, a multiple glass in which a glass on the outside of a house of a pair of glass plates has a daylighting sheet provided on a surface thereof facing a glass on the inside of the house and the glass on the inside of the house has a low-emissivity (Low-E) film provided on a surface thereof facing the glass on the outside of the house (for example, refer to PTL 1) has been known. Such a multiple glass is assumed to be applied to a new building and is hard to be applied to an existing building.
Thus, proposed is a retrofit window that achieves performance equivalent to that of a Low-E (low-emissivity) pair glass only by directly attaching the Low-E glass onto an existing window (for example, refer to PTL 2).